1. Field of the Invention
This invention relates to integrated circuit interconnects and in particular to integrated circuit interconnects adapted to propagate high frequency signals between active circuit elements.
2. Description of the Prior Art
With the advancement of very large scale integration circuit technology (VLSI), big gains in circuit speeds have been achieved. This permits a new class of integrated circuits which operate in the microwave, millimeter, and optical frequency regions, hereinafter for the sake of convenience, collectively referred to as microwaves. These advances require the introduction of new types of on-chip interconnects which can accommodate the high frequencies of operation. It is known in the art to provide interconnects such as a micro-coaxial interconnect as taught in U.S. Pat. No. 4,933,743 issued to Michael E. Thomas on Jun. 12, 1990.
The frequency requirements of these microwave circuits will eventually push well into the gigahertz range. This will especially true of bipolar emitter coupled logic devices and devices formed using gallium arsenide technology. The wavelength of a signal propagating along the interconnects in these cases can be substantially less than the edge dimensions of the die. This can cause problems with high speed interconnect coupling. Due to absorption, even optical fibers can not operate at these frequencies.
In addition, as the speed of device Operation increases, it will become necessary to match the overall circuit impedance with that of an external power source for optimal device efficiency with little reflected power. This will be especially true for very large-scale integrated microwave circuits.
It is known in the art to provide strip type waveguide systems known as microstrip lines. A microstrip line is an interconnect disposed over a large ground plane wherein a dielectric is disposed between the microstrip and the ground plane. These microstrips may serve as interconnects in the microwave frequency range. They have been applied to microwave applications within integrated circuits. It is also known how to provide impedance matching by changing the dimensions of the microstrip lines. However, the use of microstrip lines in very large scale integration applications is very difficult to implement and microstrip lines do not operate at very high frequencies without substantial degradation of fidelity.